scsi: introduce sg_io_sense_from_errno

Move more knowledge of SG_IO out of hw/scsi/scsi-generic.c, for
reusability.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/scsi/utils.h

@@ -116,6 +116,9 @@ int scsi_cdb_length(uint8_t *buf);
 #define SG_ERR_DID_TIME_OUT    0x03
 
 #define SG_ERR_DRIVER_SENSE    0x08
+
+int sg_io_sense_from_errno(int errno_value, struct sg_io_hdr *io_hdr,
+                           SCSISense *sense);
 #endif
 
 #endif